1. Field of the Invention
The present invention relates to an image sensor used for obtaining digital image data.
2. Description of the Related Art
Conventionally, linear light emitting units are often used in image reading devices such as contact-type or flatbed-type image scanners. As disclosed in JP-A-H11-55464, for example, a linear light emitting unit may comprise a light guiding member elongated in the primary scanning direction. This conventional light guiding member is configured to convert spot light (emitted from a spot light source) into linear light to irradiate a document to be read.
FIGS. 4-6 of the accompanying drawings of the present application illustrate a reference example for facilitating the understanding of the present invention. Specifically, as shown in FIG. 4, the illustrated image sensor 90 includes a resin case 91, a light guiding member 92, a lens array 93, a substrate 94 with a wiring pattern, and a sensor IC chip 95. The light guiding member 92 is formed with a reflection surface 921. The case 91 includes three supporting portions 911-913 for the light guiding member 92. FIG. 5 is a sectional view taken along lines V-V in FIG. 4, and FIG. 6 is a sectional view taken along lines VI-VI in FIG. 4. As shown in these figures, the image sensor 90 also includes a light source 96.
The image sensor 90 operates as follows. First, the light source 96 is turned on to emit light. The light is totally reflected at various portions of the surface of the light guiding member 92, while traveling in the light guiding member 92. Eventually, the light is reflected by the reflection surface 921, and emitted out of the light guiding member 92 to travel toward the document P. The light reflected by the document P is collected by the lens array 93 onto the sensor IC chip 95.
In the above reference example, a large area of the light guiding member 92 is held in contact with the case 91. As seen from FIGS. 5 and 6, each of the three supporting portions 911-913 in contact with the light guiding member 92 has substantially the same length as the light guiding member 92. With such an arrangement, the light striking on the portions where the light guiding member 92 contacts the nontransparent resin is partly absorbed by the nontransparent resin. Such light absorbance decreases the intensity of light supposed to irradiate the document P, thereby resulting in the deterioration in quality of image data outputted from the sensor IC chip 95.